1. Field of the Invention
This invention relates to an external fixation device and more particularly relates to an articulation element for the positioning and the fixation of cylindrical components such as fastening bars, rods or bone pins.
2. Description of the Prior Art
Numerous known external fixators include frames having a specific shape which allow for the location of bone pins to hold the bone fragment into which they are inserted. It is often necessary to insert the pins relatively close to nerves or arteries, which may lead to complications.
For this reason, external fixators have been developed in which the components are assembled after the pins have been inserted into the optimum position with respect to the bone fragment to be held and the tissue surrounding them. The fixation bars or rods making up the frame of the fixator are then placed between the bone pins and articulation elements are used to connect the bars and the pins. It is necessary that these articulation elements allow the bars or pins to be held at variable angulations.
European Patent EP-0,321,472 (WO-88/01152) describes an articulation element for the relative positioning of fixation bars and bone pins of an external fixator. This articulation elements includes a plurality of pairs of jaws having on their adjacent faces grooves which form a passage intended to receive a bar or a pin. Each element includes a locking element for locking the relative angular position of the jaw pairs and a clamping element passing through the pairs of jaws for clamping the bars or pins in a relative position. In addition, each jaw forming a jaw pair is respectively fitted with a positioning projection and a clearance of complementary shape.
One drawback of such a device is that it must be mounted in advance on the fixation bars or the pins which are inserted into the element via their ends. Alternatively, this type of articulation element can be removed before using it and remounted, taking care to arrange the positioning projections and positioning clearances opposite one another. In addition, so long as this device is not locked in the desired final position, the components are not held and can move with respect to one another and, in particular, the articulation element can move freely with respect to the fixation bars and the pins on which it is mounted. However, it is difficult to hold the bars, rods and pins in position before changing especially if several of these types of articulation elements are used. Consequently, it is necessary to hold the articulation element in place before clamping it to the rod or pins.